This invention relates to porous media useful in the surface tension transfer of liquids and to the fabrication of porous media structures. The achieved porous medium is useful in a variety of technical arts including the herein referred to electrical battery cell and heat pipe arts.
The transportation of liquid materials to elevated or otherwise liquid reservoir separated locations without the use of moving parts is a useful concept that is often employed in, for example, the electrical battery cell, machinery lubrication, combustion and other chemical reaction and the heat transfer arts. In each of these uses, there is need for relatively small quantities of a liquid material to be present in physical locations that are distal from the reservoir of liquid material and in conditions which are preferably free of pumps or other mechanically operated fluid displacement arrangements.
In certain of such uses, there is also present a need for effective transfer of thermal energy and for the accomplishment of such transfer in situations which may include any of the liquid, gaseous, and solid physical states of materials. Porous media, especially the porous media of the present invention, are useful in accomplishing energy transfer involving the flow and especially the recirculating flow of liquid effluents as in a heat pipe.
The patent art includes a number of examples of porous media structures and their fabrication and is indicative of the modern evolution of this art. Included in this art is the patent of K. P. Staudhammer et al, U.S. Pat. No. 3,762,011 which concerns the fabrication of a wick for use in a heat pipe. The Staudhammer patent contemplates wick preparation by the application of a slurry of high thermal conductivity particles and organic binder and organic solvent to the surface of a heat pipe. This application is followed by evaporation of the solvent and utilization of binder material surface tension properties to draw the high conductivity particles together in a bonded and compacted condition. The achievement of compacted material is followed by curing of the binder. In the Staudhammer wick structure, cured binder material is used to hold the wick together in an integral condition and to retain the wick structure in predetermined relationship with the attending heat pipe surfaces. This cured binder arrangement contrasts with the particle retention arrangement of the present invention. The Staudhammer particle size, particles of mesh size between 50 and 200 microns, and the use of an organic binder and its participation as a particle densifying mechanism also distinguish the Staudhammer structure from the present invention.
The prior patent activity also includes the patent of W. Fischer et al., U.S. Pat. No. 3,840,069 which concerns a sintered heat pipe capillary structure having a distribution of both fine pores and coarse pores. In the Fischer et al. structure, the wick pores are formed in a sintered metal powder structure by either removing one metal component of the powder grains through a chemical reaction or by an alternate oxidizing and reduction chemical treatment of the metal powder structure or by the use of metal powder having grins of different size in the powder composition.
The patent of E. A. Dancy et al, U.S. Pat. No. 4,082,863, concerns the fabrication of a ceramic heat pipe wherein is disposed a capillary layer of metal oxide ceramic material used to conduct the heat transfer fluid. In the Dancy et al. patent, a substrate member is coated with an aqueous slurry of metal oxide ceramic having a maximum particle size of about 44 microns and the slurry is covered with a granular ceramic material having a particle size in the range of 250 to 500 microns. According to a further aspect of the Dancy et al patent slurry material is also drawn up between particles and this fabrication is followed by firing of the coated surface at a temperature effecting bonded of the ceramic layer.
The Dancy et al patent is particularly directed toward the fabrication of ceramic heat pipes made from dielectric materials. The Dancy et al heat pipe contemplates use of a variety of fabrication materials including metal, glass and alumina ceramic materials with the working fluid including liquefied gases, liquid metal, hydrocarbons, fluorocarbons, ammonia, water, acetone, methanol, ethanol, the freon compounds, and other fabricated working fluids.
The Dancy et al heat pipe also contemplates use of sintered metal structures in order to achieve good heat transfer between the heat pipe capillary maze and the heat pipe container, see column 2, line 35-39. Silica is said to be an essential constituent of the mixture used in fabricating the Dancy et al structure because of its large melting point range and its resulting action as a glue between substrate and porous capillary material, see column 3, lines 57. In the Dancy et al structure, the fine particles of slurry mixture are used in order to achieve gluing action between substrate and larger particles of the slurry mixture, see column 4, lines 33-40. The ceramic substrate, use of oxide powder materials, larger particle size and gluing action of the slurry material inter alia distinguish the Dancy et al apparatus from that of the present invention.
The patent of G. Y. Eastman, U.S. Pat. No. 4,274,479, also concerns a heat pipe capillary wick structure, a structure fabricated from sintered metal--and disposed with longitudinal grooves on its interior surface. The Eastman wick grooves provide longitudinal capillary pumping while the sintered wick provides a high capillary pressure to fill the grooves and assure effective circumferential distribution of the heat transfer liquid. The Eastman patent also contemplates use of a viscous paste material for forming a wick structure, see column 4, lines 50-55. At column 4, line 16, the Eastman patent also describes the use of a hydrogen atmosphere and temperatures in the 900.degree. C. range for fabricating a copper powder based wick structure.
Other known patents of possible interest as background with respect to the present invention include U.S. Pat. Nos. 4,207,209; 4,307,164; 4,372,823; and 4,665,049.
None of these patent examples or their combination, however, suggest the porous material structure of superior liquid transporting capability and heat transfer capability of the present invention.